Military helmets, and particularly flight helmets (i.e., those worn by pilots, crew members and the like of military aircraft) have as a primary function the prevention of penetration of flying objects such as, for example, shrapnel, pieces of aircraft structure in the event of ejection or crash, and the like. However, of recent date the shell has also been serving as a mounting point for such articles as oxygen masks, microphones, earcups, and the like, and more recently precision optics which must maintain accurate alignment to the wearer's eye. It is highly desirable that the alignment be maintained during high gravity-inducing maneuvers and aerodynamic buffeting. It is for this reason that helmets carrying such optics should be custom-fitted to the contours of the head of the wearer.
Various methods and techniques are presently available for custom-fitting articles to the body parts of persons. Certain of these involve, for example, custom-fitting shoes, boots, and inserts and the like to a foot. While perhaps applicable to their intended use, many of these methods can pose problems if attempted to be used outside their intended use. For example, such techniques often require a person's body part (i.e., foot) to be placed in a container (shoe or boot), the container filled with a compound, and the compound allowed to cure to the shape of the foot over a period of time. Further, the compounds used in these techniques often include various materials and solvents that may be relatively benign when cured, but before curing and in their liquid state these compounds can be hazardous--particularly if used near the face, eyes, etc. Thus, such problems can prohibit use of certain of these techniques in connection with custom-fitting, for example, a helmet to a human head.
In addition to the toxicity posed by certain known techniques for custom-fitting, many of them are also gravity-dependent, requiring the body part (i.e., foot) to be placed into a container for surrounding by the compound. Additionally, the curing process can often approach ten minutes or more, requiring the subject to hold a position for some time.
Examples of the aforementioned techniques may be found in U.S. Pat. Nos. 3,325,919, 3,848,287 and 4,128,951.
Other custom-fitting methods use a resilient heat-softened foam of one type or another. However, the resultant heat-treated foam maintains its resiliency after cooling and, therefore, provides little in the way of energy-absorbing capability.
Another known method used in custom-fitting many of the current military helmets utilizes layers of a thermoplastic "bubble" material which softens when heated. Unfortunately, the material tends to regain its original, premolded shape with time. Examples of this technique are found in U.S. Pat. Nos. 4,412,358 and 4,432,099.
It can be seen, therefore, that a need exists for a material that can function to custom-fit one part to another, such as, for example, a helmet to the contours of the head of the user, that is safe and easy to use.